Tkinter 8.5 reference: a GUI for Python

54. Events: responding to stimuli

An event is something that happens
to your application—for example, the user presses a
key or clicks or drags the mouse—to which the
application needs to react.

The widgets normally have a lot of built-in behaviors. For
example, a button will react to a mouse click by calling
its command callback. For another example,
if you move the focus to an entry widget and press a
letter, that letter gets added to the content of the
widget.

However, the event binding capability of Tkinter allows you
to add, change, or delete behaviors.

First, some definitions:

An event is some occurrence that
your application needs to know about.

An event handler is a function
in your application that gets called when an event
occurs.

We call it binding when your
application sets up an event handler that gets called
when an event happens to a widget.